Survey instruments such as total stations are commonly used to map construction sites, record terrain features, measure land parcels, and the like. When using a total station, the surveyor typically must first determine the position and azimuthal orientation of the total station. That is, the surveyor must determine the precise geographic location of the total station, and the surveyor must also determine the direction in which the total station is pointed. This last step is often done by sighting to another reference point whose location is also know, and then calculating the angular orientation of the vector from the total station to the reference point.
A conventional approach for determining the position and azimuthal orientation of a total station is described in conjunction with Prior Art FIG. 1. In order to determine the position (e.g. latitude, longitude, and elevation) of point Z, a surveyor typically measures the distance from the total station, situated at a first known point X, to a known location at point Y. The known location at point Y is comprised, for example, of a United States Geological Service (USGS) site or landmark which has been previously surveyed and those position and elevation is precisely known. Using the two known locations, x and y, the surveyor calculates a vector location between the two points in the local coordinate system. This automatically gives the angle .theta. relative to north. Once the position and azimuthal orientation of the total station has been determined, the surveyor is then able to determine the location of point Z.
Recent attempts have been made to incorporate the capabilities of the Global Positioning System (GPS) with conventional total stations. U.S. Pat. No. 5,077,557 to Ingensand, entitled "Surveying Instrument with Receiver for Satellite Position-Measuring System and Method of Operation" filed Dec. 31, 1991, discloses a survey instrument having a single GPS receiver coupleable to the precise center of rotation thereof. Similarly, U.S. Pat. No. 5,233,357 to Ingensand et al., entitled "Surveying System Including an Electro-Optical Total Station and a Portable Receiving Apparatus Comprising a Satellite Position-Measuring System" filed Aug. 3, 1993, discloses a total station having a single GPS receiver coupleable to the precise center of rotation thereof. In both of the above-mentioned Prior Art Patents, the geographic location of the center of the total station/survey instrument is determined using GPS techniques. It will be understood by those of ordinary skill in the art, that the accuracy of the determined location of the total station/survey instrument can be improved using various methods such as differential corrections, real-time kinematics, post processing, and the like. However, such prior art survey systems still require the user to first observe a known/previously surveyed location, and then physically manipulate the total station/survey instrument to determine the azimuthal orientation of the total station with respect to north.
Hence, even though some prior art approaches simplify the process of determining the geographic location of the total station/survey instrument, conventional survey techniques and systems still require the surveyor to physically manipulate the total station/survey instrument to determine the azimuthal orientation thereof.
Thus, a need has arisen for a method and apparatus for expediently determining the azimuthal orientation of a total station without first having to observe and/or calculate the location of the total station with respect to a known site.